An example of a polyolefin-based thermoplastic elastomer composition is composed of: elastic components including a styrene block copolymer and a paraffin, naphthene, or aromatic oil; a polyolefin resin; inorganic fillers; and a resin stabilizer. Generally, such a polyolefin-based thermoplastic elastomer composition has a low hardness (shore A hardness) of about 20 to 80. A high-hardness polyolefin-based thermoplastic elastomer composition is mainly produced using a dynamically-vulcanized EPDM polyolefin resin. However, such a high-hardness polyolefin-based thermoplastic elastomer composition has problems such as difficulty in setting process conditions required for desired level of hardness, poor reproducibility of desired hardness, and difficulty in varying the composition of a blend.
Korean Patent Application No. 2007-0089916 discloses a thermoplastic elastomer composition including a thermoplastic resin, a block copolymer, and an oil. However, the composition has a shore A hardness of 20 to 80 and is unsuitable for a gasket, and post-molding shrinkage of the composition is not disclosed in this patent.
U.S. Patent Publication No. 2004-0151933 discloses a thermoplastic elastomer composition including a thermoplastic resin, a rubber elastomer, a saturated elastomer, and an oil. However, the thermoplastic elastomer composition has a low shore A hardness of about 50 and has limited applicability.